Passive infrared (PIR) sensors are commonly used for people detection in burglar alarms, automatic lights, etc. They work by detecting temperature changes that occur when a person moves into range. For example, some include a pyroelectric transducer that outputs a signal when a temperature gradient is applied across its opposite ends. Such a gradient is created when infrared (IR) radiation emitted from a moving person strikes and transfers heat to one end of the transducer before the other.
PIR sensors are sometimes mounted on a printed circuit board (PCB), proximate heat-emitting electrical components, such as lights. Heat emitted from these nearby electric components may cause temperature gradients similar to those caused by people, resulting in false detection. Continuous exposure to this energy may saturate the transducer, rendering it incapable of detection altogether.